1. Field of the Invention
The present invention relates to a linear operation type electric part which is provided in an automobile having an engine mounted therein, and which may be preferably used for a sensor for controlling a mixture ratio of fuel and air, a sensor for controlling the amount of exhaust gas to be recycled, and the like.
2. Description of the Related Art
Referring to FIGS. 11 to 13, a conventional linear operation type electric part of this kind will be described. FIG. 11 is a cross-sectional view of a conventional linear operation type electric part as viewed from the side; FIG. 12 is a cross-sectional view of the conventional linear operation type electric part as viewed from the back; and FIG. 13 is a cross-sectional view of a flat spring of the conventional linear operation type electric part. In the Figures, a box case 31 includes a housing 31a with an opened back portion, a hole 31b provided in the front portion that is in communication with the housing 31a, and a pair of guide grooves 31c provided in the front-to-back direction within the housing 31a. 
Moreover, an insulation substrate 33 having a resistive element 32 provided thereon is attached to the bottom of the housing 31a. The inside of the housing 31a is hermetically sealed by a sealing part 34, which closes the opened back portion of the housing 31a. 
A movable member 35 having a pair of shoulder parts 35a is accommodated to be linearly movable along the front-to-back direction in the housing 31a, with the pair of shoulder parts 35a being placed within a corresponding pair of housing guide grooves 31c. On the lower part of the movable member 35 is attached, at least one sliding member 36 which slides against and is in electrical contact with the resistive element 32. Moreover, a flat spring 37 as shown in FIG. 13 is provided on an upper part of the movable member 35. The flat spring 37 presses down the movable member 35 so that the lower part of the movable member 35 elastically abuts with the case 31 to prevent backlash along the vertical direction A. At the same time, the flat spring 37 prevents backlash along the horizontal width direction B.
A coil spring 38, for biasing movable member 35 toward the front of the housing 31a and for restoring movable member 35 from backward movement, is placed between the movable member 35 and the sealing part 34. An operation shaft 39 is inserted into the hole 31b such that backward linear movement of the operation shaft 39 along the horizontal front-to-back axial direction of housing 31a causes the movable member 35 to also move linearly backward along the axial direction.
Specifically, the spring force of the coil spring 38 acts in the same direction as the axial direction of the operation shaft 39 whereas the spring force of the flat spring 37 acts in directions perpendicular to the axial direction.
Furthermore, the conventional linear operation type electric part operates as follows. First, as the operation shaft 39 is pressed backward along the axial direction, the movable member 35 moves toward the back against the action of coil spring 38.
Thus, the sliding member 36 moves on the resistive element 32 together with the movable member 35 to produce a varying resistance value, and thus enabling detection of the position of sliding member 36.
Moreover, during the movement of the movable member 35, the flat spring 37 moves together with the movable member 35 while sliding along the case 31. At the same time, the lower part of the movable member 35 moves while in slidable contact with the case 31.
When the pressure on the operation shaft 39 is released, the movable member 35 on which the sliding member 36 is attached and the operation shaft 39 are pushed frontward by the biasing force of coil spring 38 so as to restore them to their original state.
The conventional linear operation type electric part requires the flat spring 37 to prevent backlash of the movable member 35 along the vertical and horizontal directions in addition to the coil spring 38 for restoring the movable member 35 from its backward movement. In other words, there is a need for two kinds of spring parts, i.e., the coil spring 38 and the flat spring 37. The increased number of parts leads to an increased cost.
Moreover, placing the flat spring 37 inside the guide grooves 31c requires cumbersome attachment work, and thus detracts from fabrication productivity. In addition, the flat spring 37 and the case 31 are in slidable contact with each other, so that the movable member 35 cannot move smoothly.
In view of above, it is an object of the present invention to provide a linear operation type electric part in which a spring member for restoring the movement of a movable member and a spring member for preventing the backlash of the movable member are formed of the same kind of coil spring, thereby reducing the number of parts used therefore, and enabling lower cost and increased productivity, and in which the movable member can be moved smoothly.
As first means to solve the above-described problems, the structure according to the present invention comprises: an operation shaft linearly movable along an axial direction; a movable member abutting with one end of the operation shaft, the movable member being disposed so as to be linearly movable by the operation shaft; a spring member for biasing the movable member so as to be restored from movement thereof; a case having a guide part for guiding the movable member during the movement thereof; and a detection means disposed on the movable member and operated by the movement of the movable member. The guide part of the case comprises an upper guide sub-part and a lower guide sub-part for guiding surfaces of the movable member from above and below, respectively. The movable member comprises: a lower slide-contact part having the detection means on a lower side thereof and sliding in contact with the lower guide sub-part; and an upper slide-contact part located above and opposing to the lower slide-contact part, the upper slide-contact part sliding in contact with the upper guide sub-part. The upper and lower guide sub-parts and the upper and lower slide-contact parts form a restriction mechanism for restricting the movement of the movable member. The movable member receives from the spring members a turning moment for skewing a center line of the movable member in direction different to the axial direction, the center line extending along a front-to-back direction from a center of the movable member, thus rotating the movable member with respect to the axial direction, the rotation causing the upper and lower slide-contact parts of the movable member to press against and be in contact with their corresponding upper and lower guide sub-parts of the case, respectively. The restriction mechanism restricts the movement of the movable member along the vertical and width directions to prevent a backlash of the movable member. The movable member linearly moves while being skewed with respect to the axial direction.
As second means to solve the problems, the restriction mechanism has inclined planar surfaces on each of the upper and lower guide sub-parts or on each of the upper and lower slide-contact parts.
As third means to solve the problems, the restriction mechanism has inclined planar surfaces on each of the upper guide sub-parts and the upper slide-contact parts or on each of the lower guide parts and the lower slide-contact parts.
As fourth means to solve the problems, the restriction mechanism has s the surfaces of one of either a pair of the upper guide sub-parts and the upper slide-contact parts or a pair of the lower guide sub-parts and the lower slide-contact parts formed of inclined planar surfaces capable of abutting with each other, respectively, while the other pair comprises one arc-shaped surface and one flat surface abutting with the arc-shaped surface.
As fifth means to solve the problems, the restriction mechanism comprises first and second restriction mechanisms provided on left and right sides along the width direction perpendicular to the axial direction of the operation shaft.
As sixth means to solve the problems, one of a first and second restriction mechanisms is positioned near the operation shaft while the other of the first and second restriction mechanisms is positioned farther from the operation shaft than the one of the first and second restriction mechanisms.
As seventh means to solve the problems, the turning moment of the movable member is generated by a spring member comprising one coil spring.
As eighth means to solve the problem, the turning moment of the movable member is generated by a pair spring members comprising coil springs disposed on left and right sides along the width direction of the operation shaft.
As ninth means to solve the problems, a force applied to the movable member by each of the two coil springs is controlled by differentiating the respective distances between the position at which each coil spring abuts with the movable member and the corresponding position at which each coil spring abuts with the case.
As tenth means to solve the problems, the two coil springs are disposed at positions on a line extending perpendicularly to the axial direction of the operation shaft.
As eleventh means to solve the problems, the movable member is in elastic contact with the operation shaft due to an action of the spring members.
As twelfth means to solve the problems, the restriction mechanism is formed of an inclined planar surface on at least one of the upper guide sub-parts and the upper sliding parts, a flat surfaced on one of the lower guide sub-part and the lower sliding parts, and a flat surface or at least one pair of convex portions in contact with the flat surface provided on another lower guide sub-part and the lower sliding part.
As thirteenth means to solve the problems, the restriction mechanism is formed of a inclined planar surface on at least one of the lower guide sub-parts and the lower sliding parts, a flat surface on one of the upper guide sub-parts and the upper sliding parts, and a flat surface or at least one pair of convex portions in contact with the flat surface provided on another upper guide sub-part and the upper sliding part.
As fourteenth means to solve the problems, the restriction mechanism comprises opposing inclined planar surfaces provided on the upper guide sub-parts and on the upper slide-contact parts, and opposing inclined planar surfaces on the lower guide sub-parts and the lower slide-contact parts, so that each pair of corresponding inclined planar surfaces is kept in elastic contact by the turning moment applied by the spring member.
As fifteenth means to solve the problems, the spring assembly comprises a first and a second spring member for biasing the operation shaft so as to be restored from the backward movement thereof, wherein the second spring member is formed of one coil spring for pushing the movable member in a restoring direction at a position offset from the central axis.
As sixteenth means to solve the problems, prolonged arm parts, each extending toward outer ends along the width direction of the movable member and perpendicular to the axial direction, are provided on the operation shaft at an end contacting the movable member, each prolonged arm part being in contact with one of the first spring members, such that a pair of the first springs are provided at the outer ends along the width direction of the movable member so as to impart opposing turning moments on the operation shaft.